Edit in JSFiddle

var createPet = function(name) {
  var sex;
  
  return {
    setName: function(newName) {
      name = newName;
    },
    
    getName: function() {
      return name;
    },
    
    getSex: function() {
      return sex;
    },
    
    setSex: function(newSex) {
      if(typeof newSex == "string" && (newSex.toLowerCase() == "male" || newSex.toLowerCase() == "female")) {
        sex = newSex;
      }
    }
  }
}

var pet = createPet("Vivie");

var pet_getname = pet.getName();
console.log(pet_getname);

pet.setName("Oliver");
pet.setSex("male");

var pet_getsex = pet.getSex();
console.log(pet_getsex);

var pet_getname = pet.getName();
console.log(pet_getname);